The human eye is able to interpret very many different colours. Colour may be considered to be the combined effect of three distinct components or properties of light: hue, saturation and brightness. Hue is the name of the colour, and places the colour in its correct position in the electromagnetic spectrum. Saturation is the degree of intensity, or strength, of a colour. Brightness describes differences in the intensity of light reflected from, or, transmitted by, a colour image.
In colour television systems, video signals are represented by three components: Y (luminance), and two chrominance components (Cb, Cr). The signal is thus referred to as YCbCr. The luminance component (Y) contains the brightness information, and the chrominance components (Cb, Cr) contain the colour information.
The YCbCr system is defined in CCIR601, which relates to a worldwide digital video standard. In an 8-bit digital system, Y has a normal range of 16 to 235, and Cb and Cr have a range of 16 to 240, with 128 equalling 0.
The YCbCr colour space is represented graphically in FIG. 1. The values of Y, Cb and Cr are shown without the offsets described above i.e. the range of Y is 0 to 219, and the range of Cb and Cr is −112 to 112. In the colour space as illustrated, the hue is represented by the phase angle with respect to the Cb axis. The magnitude of the chrominance components vector, in combination with the luminance Y, provides a measure for colour saturation